Chapter 34
Vocabulary Potential Difference- The difference in electric potential (voltage) between two points. Free charge flows when there is a difference, and will continue until both points reach a common potential. Electric Current- The flow of electric charge; measured in amperes (coulombs per second). Amperes- SI unit of electric current. A flow of one coulomb of charge per second is one ampere (symbol A). Voltage Source- A device, such as a dry cell or generator, that provides a potential difference. Ohm’s Law- The statement that the current in a circuit is directly proportional to the voltage impressed across the circuit, and is inversely proportional to the resistance of the circuit. Alternating Current- (ac) Electric current that repeatedly reverses in direction, twice each cycle. Usually at 60 cycles per second, of hertz (Hz), in North America, of 50 hertz elsewhere. Direct Current- (dc) Electric current whose flow of charge is always in one direction. Diode- A tiny electric device that acts as a one-way valve to allow electron flow in only one direction. Electric Power- The rate at which electric energy is converted into another form, such as light, heat, or mechanical energy (or converted from another form into electric energy).
34.1 - Flow of Charge
The flow of an electric charge will continue as long as there is a potential difference present.
If the potential difference is from a charged object the flow will be short. If the potential difference is from a generator or a battery then the flow will continue for a longer period of time.
34.2 - Electric Current
The charge in electric current is carried in a solid conductor by electrons that can easily move through the conductor.
Electric Current is measured in amperes.
Wire's that carry current have a neutral charge because the same amount of electrons that enter at one end, leave at the other end.
34.3 - Voltage Sources
Examples of voltage sources - Batteries, Generators, Anything that will cause a continuous flow of charges.
34.4 - Electric Resistance
Long and thin wires have more resistance than short and thin wires.
Materials of high conductivity have a low resistance.
Resistance is measured in Ohm's.
34.5 - Ohm's Law
Taken from "Physics Review Notes" by Tom Strong
To solve for the variable you want to you can put your finger over the variable you want, and the remaining two variables are in the correct alignment for the equation. For example of you cover the R with your finger, you see
This is the equation to solve for resistance.
Example of Ohm's Law
A nine volt battery supplies power to a cordless curling iron with a resistance of 18 ohms. How much current is flowing through the curling iron?
Vocabulary
Potential Difference- The difference in electric potential (voltage) between two points. Free charge flows when there is a difference, and will continue until both points reach a common potential.
Electric Current- The flow of electric charge; measured in amperes (coulombs per second).
Amperes- SI unit of electric current. A flow of one coulomb of charge per second is one ampere (symbol A).
Voltage Source- A device, such as a dry cell or generator, that provides a potential difference.
Ohm’s Law- The statement that the current in a circuit is directly proportional to the voltage impressed across the circuit, and is inversely proportional to the resistance of the circuit.
Alternating Current- (ac) Electric current that repeatedly reverses in direction, twice each cycle. Usually at 60 cycles per second, of hertz (Hz), in North America, of 50 hertz elsewhere.
Direct Current- (dc) Electric current whose flow of charge is always in one direction.
Diode- A tiny electric device that acts as a one-way valve to allow electron flow in only one direction.
Electric Power- The rate at which electric energy is converted into another form, such as light, heat, or mechanical energy (or converted from another form into electric energy).
34.1 - Flow of Charge
- The flow of an electric charge will continue as long as there is a potential difference present.
- If the potential difference is from a charged object the flow will be short. If the potential difference is from a generator or a battery then the flow will continue for a longer period of time.
34.2 - Electric Current- The charge in electric current is carried in a solid conductor by electrons that can easily move through the conductor.
- Electric Current is measured in amperes.
- Wire's that carry current have a neutral charge because the same amount of electrons that enter at one end, leave at the other end.
34.3 - Voltage Sources- Examples of voltage sources - Batteries, Generators, Anything that will cause a continuous flow of charges.
34.4 - Electric Resistance- Long and thin wires have more resistance than short and thin wires.
- Materials of high conductivity have a low resistance.
- Resistance is measured in Ohm's.
34.5 - Ohm's Law- To solve for the variable you want to you can put your finger over the variable you want, and the remaining two variables are in the correct alignment for the equation. For example of you cover the R with your finger, you see
Example of Ohm's LawThis is the equation to solve for resistance.
A nine volt battery supplies power to a cordless curling iron with a resistance of 18 ohms. How much current is flowing through the curling iron?
I = 0.5 Amps
(http://www.grc.nasa.gov/WWW/K-12/Sample_Projects/Ohms_Law/ohmslaw.html)
34.6 - Ohm's Law and Electric Shock
- When your skin is dry it has a resistance of 500,000 Ω.
- If your skin is soaked in salt water your skin's resitance can become 100 Ω.
- The smallest current that can be felt is .001A.
- A .005 A current starts to be painful.
- A .070 A can be fatal if it passes through your heart.
34.7 - Direct Current and Alternating Current- Direct Currents are usually currents from batteries or charged objects.
- Alternating current is usually used to deliver.
34.8 - Converting AC to DC- Diodes can be used to pass only a part of an AC current and change it into a DC source.
34.9 - The speed of Electrons in a Circuit- As soon as a circuit is completed, electricity begins to flow.
- Individual electrons take a lot longer to move around a circuit. The drift speed is usually about 1 meter every 3 hours.
34.10 - The Source of Electrons in a Circuit- The potential difference in a circuit doesn't supply the electrons, it just makes the electrons move.
- The electrons in the circuit start out in the circuit, they are already present in the wires and other components.
34.11 - Electric Power